Add AlphaThreshold filter.

gm/imagealphathreshold.cpp

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "gm.h"
+#include "SkAlphaThresholdFilter.h"
+#include "SkRandom.h"
+
+#define WIDTH 500
+#define HEIGHT 500
+
+namespace skiagm {
+
+class ImageAlphaThresholdGM : public GM {
+public:
+    ImageAlphaThresholdGM() {
+        this->setBGColor(0xFFFFFFFF);
+    }
+
+protected:
+    virtual uint32_t onGetFlags() const SK_OVERRIDE {
+        return this->INHERITED::onGetFlags() | GM::kSkipTiled_Flag;
+    }
+
+    virtual SkString onShortName() SK_OVERRIDE {
+        return SkString("imagealphathreshold");
+    }
+
+    virtual SkISize onISize() SK_OVERRIDE {
+        return make_isize(WIDTH, HEIGHT);
+    }
+
+    virtual void onDraw(SkCanvas* canvas) SK_OVERRIDE {
+        SkIRect rects[2];
+        rects[0] = SkIRect::MakeXYWH(0, 150, WIDTH, HEIGHT - 300);
+        rects[1] = SkIRect::MakeXYWH(150, 0, WIDTH - 300, HEIGHT);
+        SkRegion region;
+        region.setRects(rects, 2);
+
+        SkPaint paint;

[bsalomon, 2013/12/18 14:38:12]

Can we make the GM somehow test that the filter respects the canvas's matrix?

[Zachary Kuznia, 2013/12/19 01:28:40]

Done.

+        paint.setImageFilter(
+            SkAlphaThresholdFilter::Create(region, 0.2f, 0.7f))->unref();
+        canvas->saveLayer(NULL, &paint);
+        paint.setAntiAlias(true);
+
+        SkPaint rect_paint;
+        rect_paint.setColor(0xFF0000FF);
+        canvas->drawRect(SkRect::MakeXYWH(0, 0, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0xBFFF0000);
+        canvas->drawRect(SkRect::MakeXYWH(WIDTH / 2, 0, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0x3F00FF00);
+        canvas->drawRect(SkRect::MakeXYWH(0, HEIGHT / 2, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        rect_paint.setColor(0x00000000);
+        canvas->drawRect(SkRect::MakeXYWH(WIDTH / 2, HEIGHT / 2, WIDTH / 2, HEIGHT / 2),
+                         rect_paint);
+        canvas->restore();
+    }
+
+private:
+    typedef GM INHERITED;
+};
+
+//////////////////////////////////////////////////////////////////////////////
+
+static GM* MyFactory(void*) { return new ImageAlphaThresholdGM; }
+static GMRegistry reg(MyFactory);
+
+}